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| Titel |
Observation of 2nd Schumann eigenmode on Titan's surface |
| VerfasserIn |
C. Béghin, G. Wattieaux, R. Grard, M. Hamelin, J. P. Lebreton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2193-0856
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Instrumentation, Methods and Data Systems ; 2, no. 2 ; Nr. 2, no. 2 (2013-10-22), S.237-248 |
| Datensatznummer |
250084922
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| Publikation (Nr.) |
 copernicus.org/gi-2-237-2013.pdf |
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| Zusammenfassung |
| This work presents the results obtained from an updated data analysis of
the observations of extremely low frequency (ELF) electromagnetic waves
performed with the HASI-PWA (Huygens Atmospheric Structure and Permittivity,
Wave and Altimetry) instrumentation after Huygens Probe landing on Titan's
surface in January 2005. The most significant signals observed at around 36 Hz
throughout the descent in the atmosphere have been extensively analyzed
for several years, and subsequently interpreted as the signature of a
Schumann resonance, although the latter exhibits atypical peculiarities
compared with those known on Earth. The usual depicting methods of space
wave data used so far could not allow for retrieving the presence of weak
signals when Huygens was at rest for 32 min on Titan's surface. Whereas
the expected signal seems hidden within the instrumental noise, we show that
a careful statistical analysis of the amplitude distribution of the 418
spectral density samples of the 36 Hz line reveals abnormal characteristics
compared to other frequencies. This behavior is shown to occur under
propitious circumstances due to the characteristics of the onboard data
conversion processes into digital telemetry counts, namely 8-bit dynamic
after logarithm compression of the DFT (Discrete Fourier Transform) of ELF
waveforms. Since this phenomenon is observed only at the frequency bin
around 36 Hz, we demonstrate that the Schumann resonance, seen in the
atmosphere within the same band is still present on the surface, albeit
with a much smaller amplitude compared to that measured before and a few
seconds after the impact, because the electric dipole is thought to have
been stabilized ten seconds later almost horizontally until the end of the
measurements. |
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